Process for making refractory metal material

ABSTRACT

An improved process for making refractory metal material is disclosed wherein in the process of manufacturing the material, the additional steps of treating the material in a liquid anhydrous sodium hydroxide bath, in a nitric acid bath, and finally in a hot water bath for specified periods of time are incorporated into the process.

United States Patent [151 3,649,260

Denniston et al. 1 Mar. 14, 1972 [54] PROCESS FOR MAKING REFRACTORY 3,171,755 3/1965 Reuschel et al ..156/l7 METAL MATERIAL 3,030,239 4/1962 Mekjean et a1. 134/29 3,011,923 12/1961 Coffer ....l34/27 [72] Inventors: Davi M- Denniston, n vi 3,232,803 2/1966 Barnett ..134/3 Shanks, Granville Summit; Neville H. Regggifl 6/1947 Spence et a1 134/27 Simpson, Towanda, all of Pa. Primary Examiner-Carl D. Quarfonh [73] Asslgnee. Sylvama Electric Products Inc. Assistant Examiner R. E Schafer [22] Filed: Feb. 27, 1970 Attorney-Norman J. OMalley, Donald R. Castle and William H. McNeil] [21] Appl. No.: 14,932

ABSTRACT U.S. An improved process for making refractory meta] material is 134/23, l34/29, 134/3 134/41 disclosed wherein in the process of manufacturing the materi- [51] Int. Cl. "1322 3/24 a], the additional steps of treating the material in a liquid an- Field of Search ..75/2l3, 1; 134/27, 2 hydrous sodium hydroxide bath, in a nitric acid bath, and 134/29, 3, 2, 41 finally in a hot water bath for specified periods of time are incorporatcd into the process.

[56] References Cited 7 Claims, 1 Drawmg Figure UNITED STATES PATENTS d A H v e 1 we 31391658 7/1964 rs n l r w l j7313133.237 Q0972..

' l4 12 IO 18 16x LIQUID ANHYDROUS HOT WATER NITRIC ACID SOD HYDROXIDE TREATMENT TREATMENT TREATMENT PROCESS FOR MAKING REFRACTORY METAL MATERIAL CROSS-REFERENCE TO RELATED APPLICATIONS Copending U.S. Pat. application entitled Wire Cleaning Machine," Ser. No. 15,010 filed concurrently herewith pertains to a machine suitable for use in one aspect of this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved method of making refractory metal material. More specifically, it relates to a method of making refractory metal material, wherein additional steps of treating said material is incorporated into the process of manufacturing said material. The method of producing the refractory material may include processes wherein a metal oxide is converted to a metal powder, pressed into bars, annealed, presintered, hydrogen reduced, swaged and made into a desired form.

2. Description of the Prior Art In the manufacture of refractory metal material, it is often desirable to remove all surface contamination to insure that no oxide scale is present, to enhance appearance, i.e., have a shiny surface, and in the case of wire and ribbon, to insure even deposition rates when said material is coated by pyrolytic deposition processes. The methods heretofore used have many disadvantages. For example, methods used to clean refractory metal sheet and plate include:

1. blasting said material with iron balls,

2. brushing said material with iron brushes,

3. using suitable commercial cleaners, and

4. heating said material in hydrogen.

Inherent disadvantages of the above-mentioned methods include l. uneven, or incomplete cleaning,

2. additional problem of removing iron and oxide scale residues,

3. expense, and

4. change in some of the desirable properties such as surface appearance, smoothness, tensile strength and ductility.

Similar methods are used to clean refractory metal wire and ribbon. For example, one method used to clean the wire and ribbon was to heat said wire to a specified temperature in a hydrogen furnace. While this method cleaned the wire and ribbon, it also cleaned the tensile strength of said wire and said ribbon to fall below standard accepted strengths. Another method employed the use of electrocaustic cleaning wherein an electric current was passed through a caustic solution and the difference in the potential between the wire and ribbon submersed in said caustic solution and said caustic solution caused the wire and ribbon to be etched. Although the above described method removed some of the surface contaminants, said method also had several disadvantages. For example, the etching could not be controlled and diameter variation of said wire and said ribbon resulted. This method also changed the surface condition, so that other desirable substances could not be deposited on said wire and said ribbon.

Other methods that have been tried but have serious disadvantages include treating the as-drawn wire and ribbon with a nitric acid-hydrofluoric acid bath and treating the as-drawn wire and ribbon with a sodium hydroxide solution. Neither of these two methods were satisfactory for one or more of the following reasons:

1. excessive etching of said wire and ribbon,

2. nonuniform etching of said wire and ribbon,

3. failure to remove surface contaminants from said wire and ribbon, and

4. use of hazardous materials requiring special handling.

It is believed, therefore, that a process which completely removes surface contaminants from refractory metal material, especially tungsten and molybdenum wire, without causing uneven etching of said material, without preventing subsequent deposition by other desirable substances, and without altering the desirable characteristics of said material, such as, for example, tensile strength and ductility, by a relatively safe, non-hazardous operation is an advancement in the art.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention, there is provided a process comprising treating the surface of the refractory metal material in l. a liquid anhydrous sodium hydroxide bath at a temperature of at least about 350 C. for a period from about 8 milliseconds to about 16 milliseconds,

2. a nitric acid bath at a concentration of no greater than about 8 N for a period of from about 2.6 milliseconds to about 5.3 milliseconds, and thereafter 3. a water bath of at least about C. for a period of at least about 16 milliseconds.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE illustrates the flow sheet representing a typical continuous process of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above description of one of the aspects of this invention and the above described drawing.

An improved process for making refractory metal material is achieved by treating said material with a liquid anhydrous sodium hydroxide bath, followed by a nitric acid bath, and finally with a hot water bath.

While said process can be used on most refractory metal materials, it is generally preferred to use said process on sheet, plate, and wire. Especially preferred are tungsten wire and molybdenum wire.

Sodium hydroxide pellets heated to a temperature of at least about 350 C. is the preferred source of liquid anhydrous sodium hydroxide. At temperatures below about 350 C., said NaOl-I tends to set up or solidify, which causes breakage of wire. Although temperature greater than about 450 C. can be used, said NaOH can become a safety hamrd because of the fumes given off and by the spattering of said NaOH.

In the second treatment, nitric acid at room temperature and at a concentration of not greater than about 8 N is generally employed. Care must be taken not to go above about 8 N to insure that the proper reaction takes place between said acid solution and the metal wire.

Water at a temperature of at least about 80 C. is employed to rinse any residue formed from the two previously mentioned treatments. Below about 80 C. dissolution of residues is incomplete. Temperatures above the boiling point of water under atmospheric conditions are generally unnecessary. Without said water treatment, a reaction can continue between the residue and wire after said wire is wound on spools. Because of the continued reaction, it is especially critical in wire production that said water wash step should be from about 6 milliseconds to about 16 milliseconds after said nitric acid treatment.

As can be seen by anyone skilled in the art, the treatment time in each stage is critical. Treatment times from about 8 milliseconds to about 16 milliseconds for said liquid anhydrous NaOH bath, from about 2.6 milliseconds to about 5.3 milliseconds for said nitric acid bath, and for at least about 16 milliseconds for said water bath are preferred. Any length of time beyond said 16 milliseconds can be used in the hot water wash step; however, times beyond about 26 milliseconds are generally avoided as they needlessly detract from the overall processing time.

For example, if the refractory metal material is about 0.0005-mil tungsten wire being continuously drawn at a rate from about to about 130 fi./min.. the preferred treatment times are about 9.8 milliseconds to about 12.7 milliseconds in the NaOH bath. from about 3.3 milliseconds to about 4.2 milliseconds in the nitric acid bath, from about l9.6 milliseconds to about 25.4 milliseconds in the hot water bath, and a total treatment time of not greater than about 45 milliseconds. It is preferred for practical design reasons to have the above-mentioned process on a continuous basis.

in order to more fully illustrate the present invention. the following non-limiting example is given. All parts, proportions and percentages are by weight unless otherwise given.

EXAMPLE 1 in particular reference to the FIGURE, a flow sheet of a typieal continuous process is given in which the system consists of an advancement means 10, a liquid anhydrous sodium hydroxide bath 12, a nitric acid bath 14, a hot water bath l6 and a guide means 18.

in a typical example, as-drawn tungsten wire, 0.0005 inches in diameter and drawn at a rate of speed from about 100 to about 130 ft./min., goes over an advancement means 10 to insure proper tension and into a molten caustic bath 12 at a temperature of at least about 350 C., the total length of wire treated at one time being about 3 inches. Said as-drawn wire is then treated in a nitric acid bath 14 at a concentration of not greater than about 8 N, the total length of wire treated at one time being about 1 inch. Said as-drawn wire is then treated to a water bath 16 at a temperature of at least 82 C., the total length of wire treated at one time being about 6 inches, before being drawn over a guide means 18, and drawn on suitable bontainers such as being wound on spools.

Tests are made for surface contaminants by running said treated wire through a chamber at a temperature of about 1,340" (3., at about I20 volts, and at about 56 amps and by bhecking small strips of treated wire under a microscope. No surface contaminants are observed.

liiimilar treatments and subsequent tests are conducted on molybdenum wire with substantially the same results.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. In the process of manufacturing refractory metal forms from refractory metal material, wherein a metal oxide is converted to metal powder, pressed into bars, annealed, presintered, hydrogen reduced. swaged, and made into the desired form, the improvement comprising the subsequent and additional steps of a. treating the surface of said form in a liquid anhydrous todium hydroxide bath at a temperature of at least about 350 C. for a period from about 8 milliseconds to about .6 milliseconds,

. followed by treating the surface of said form in a nitric acid bath at a concentration of no greater than about 8 N for a period of time from about 2.6 milliseconds to about 15.3 milliseconds, and

thereafter treating the surface of said form in a water bath at a temperature of at least about 80 C. for a period of at least about 16 milliseconds.

.2. An improvement according to claim 1, wherein said tetractory metal material is selected from the group consisting of tungsten, molybdenum and mixtures thereof.

.3. An improvement according to claim 2, wherein said form 18 wire.

4. An improvement according to claim 3, wherein said sodium hydroxide treating time is from about 9.8 milliseconds to about 12.7 milliseconds, wherein said nitric acid treating time is from about 3.3 milliseconds to about 4.2 milliseconds,

wherein said hot water treating time is from about 19.6 milliseconds to about 25.4 milliseconds, wherein time between 531d nitric acid treatment and said hot water treatment is from about 6 milliseconds to about 16 milliseconds, and wherein total treatment time IS less than about milliseconds.

5. An improvement according to claim 4, wherein said form is molybdenum wire.

IS. An improvement according to claim 4, wherein said form is tungsten wire.

'7. An improvement according to claim 4, wherein said process is continuous.

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2. An improvement according to claim 1, wherein said refractory metal material is selected from the group consisting of tungsten, molybdenum and mixtures thereof.
 3. An improvement according to claim 2, wherein said form is wire.
 4. An improvement according to claim 3, wherein said sodium hydroxide treating time is from about 9.8 milliseconds to about 12.7 milliseconds, wherein said nitric acid treating time is from about 3.3 milliseconds to about 4.2 milliseconds, wherein said hot water treating time is from about 19.6 milliseconds to about 25.4 milliseconds, wherein time between said nitric acid treatment and said hot water treatment is from about 6 milliseconds to about 16 milliseconds, and wherein total treatment time is less than about 45 milliseconds.
 5. An improvement according to claim 4, wherein said form is molybdenum wire.
 6. An improvement according to claim 4, wherein said form is tungsten wire.
 7. An improvement according to claim 4, wherein said process is continuous. 